Using data from the Japan-led XRISM (X-ray Imaging and Spectroscopy Mission) observatory, astronomers have directly observed a giant star’s outflow, called a stellar wind, being captured by its compact companion and providing the power source for strong X-ray flares. The research is part of NASA’s exploration of the extreme universe to better understand how the cosmos works. “We’ve never before seen clear indications of wind plasma falling onto a compact object,” said Roi Rahin, a researcher at UMBC (University of Maryland, Baltimore County) and NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We can now test our understanding of these processes in much greater detail.” A paper describing the findings published Friday in the journal Science Advances. The target system is BP Crucis, a high-mass X-ray binary located about 13,000 light-years away in the southern constellation Crux. The primary star, known as Wray 977, is a blue hypergiant about 40 times the Sun’s mass and 60 times its size. It’s so big, hot, and luminous that ionized gas constantly streams away from it, a phenomenon astronomers call a stellar wind.
天文学家利用日本领导的 XRISM（X 射线成像和光谱任务）天文台的数据，直接观察到一颗巨大恒星的流出，称为恒星风，被其紧凑的伴星捕获，并为强烈的 X 射线耀斑提供了动力来源。这项研究是美国宇航局探索极端宇宙的一部分，目的是更好地了解宇宙是如何运作的。 UMBC（马里兰大学巴尔的摩分校）和 NASA 位于马里兰州格林贝尔特的戈达德太空飞行中心的研究员 Roi Rahin 表示：“我们以前从未见过风等离子体落在致密物体上的明确迹象。” “我们现在可以更详细地测试我们对这些过程的理解。”周五发表在《科学进展》杂志上的一篇描述研究结果的论文。目标系统是 BP Crucis，一个位于南十字座约 13,000 光年之外的高质量 X 射线双星系统。主恒星名为 Wray 977，是一颗蓝超巨星，质量约为太阳的 40 倍，大小约为太阳的 60 倍。它是如此巨大、炽热和明亮，以至于电离气体不断地从它身边流走，天文学家将这种现象称为恒星风。
The supergiant’s companion is a tiny-but-mighty neutron star called GX 301-2. The crushed core of a star that long ago exploded as a supernova, it packs more than the Sun’s mass into a ball roughly 12 miles (20 kilometers) across. Rotating every 11 minutes, it sweeps an X-ray beam toward Earth, which classifies it as a pulsar. Twice during the pulsar’s 41.5-day orbit, near its closest and farthest points from the primary star, strong X-ray flares occur for several days. Astronomers think the pulsar’s gravitational influence on the star creates an especially dense stream of plasma. Flares occur when the pulsar traverses this stream and captures some of its matter. The strongest eruptions happen closer to the star, where the stream is denser. The researchers targeted the system with XRISM on Feb. 1, 2025, observing it for about 16 hours near the end of one of these stronger flares. The observatory’s Resolve instrument, jointly developed by NASA and JAXA (Japan Aerospace Exploration Agency), captured highly detailed X-ray spectra, revealing rapidly changing emission and absorption lines. In particular, absorption lines from highly ionized iron revealed the speed and direction of plasma relatively close to the pulsar.
这颗超巨星的伴星是一颗微小但强大的中子星，名为 GX 301-2。一颗很久以前作为超新星爆炸的恒星的破碎核心，将超过太阳的质量压缩成一个直径约 12 英里（20 公里）的球体。它每 11 分钟旋转一次，向地球发射 X 射线束，地球将其归类为脉冲星。在脉冲星 41.5 天的轨道上，在距主星最近和最远的点附近，两次出现持续数天的强烈 X 射线耀斑。天文学家认为脉冲星对恒星的引力影响会产生特别密集的等离子体流。当脉冲星穿过该流并捕获其中的一些物质时，就会发生耀斑。最强烈的喷发发生在靠近恒星的地方，那里的气流更密集。研究人员于 2025 年 2 月 1 日用 XRISM 瞄准了该系统，在其中一次较强耀斑即将结束时对其进行了约 16 小时的观察。该天文台的 Resolve 仪器由 NASA 和 JAXA（日本宇宙航空研究开发机构）联合开发，捕获了高度详细的 X 射线光谱，揭示了快速变化的发射线和吸收线。特别是，高度电离铁的吸收线揭示了相对接近脉冲星的等离子体的速度和方向。
When Rahin first saw these spectra, he realized he hadn’t seen anything like them before. He scoured the scientific literature for similar observations and came up empty-handed.
当拉辛第一次看到这些光谱时，他意识到自己以前从未见过类似的东西。他在科学文献中搜寻类似的观察结果，但一无所获。
“It was clear that these observations were groundbreaking, but at the same time this meant the analysis had to be especially detailed,” said Nazma Islam, a co-author formerly at UMBC and NASA Goddard and now an assistant professor at Manipal Centre for Natural Sciences, India. “We could see how the dense stream of plasma acts very close to the neutron star.”
“很明显，这些观察结果是开创性的，但同时这意味着分析必须特别详细，”纳兹玛·伊斯兰 (Nazma Islam) 说，她曾是 UMBC 和 NASA 戈达德中心的合著者，现在是印度马尼帕尔自然科学中心的助理教授。 “我们可以看到密集的等离子体流如何在非常靠近中子星的地方起作用。”
Rahin and his team show that the iron absorption lines they observed are displaced to lower energies than they would be if measured in a laboratory. This displacement, called a redshift, indicates motion away from the observer, which means the gas is flowing toward the pulsar. The extent of the redshift indicates the plasma’s velocity. The team’s analysis indicates gas is racing toward the pulsar at speeds of around 335,000 mph (540,000 kph). Here’s what the researchers think is going on: As the pulsar enters the stream, it sweeps up gas into a thick, messy, turbulent disk. This gas spirals down to the pulsar, heats up, and emits X-rays to power the flares. As the pulsar pushes farther into the stream, the turbulent disk breaks down. Astronomers suspect that as the pulsar moves more directly into the flow, the stream no longer has the angular momentum required to maintain the disk. Once the disk dissipates, plasma flows directly onto the neutron star. Observations with XRISM occurred near the end of this phase.
拉辛和他的团队表明，他们观察到的铁吸收线的能量比在实验室测量的要低。这种位移称为红移，表明远离观察者的运动，这意味着气体正在流向脉冲星。红移的程度表明等离子体的速度。该团队的分析表明，气体正以大约 335,000 英里/小时（540,000 公里/小时）的速度冲向脉冲星。研究人员认为正在发生的事情是这样的：当脉冲星进入流时，它会将气体扫成一个厚厚的、混乱的、湍流的圆盘。这种气体螺旋下降到脉冲星，升温并发射 X 射线为耀斑提供动力。当脉冲星进一步推入流中时，湍流盘就会破裂。天文学家怀疑，随着脉冲星更直接地进入气流，气流不再具有维持圆盘所需的角动量。一旦圆盘消散，等离子体就会直接流到中子星上。 XRISM 的观察发生在该阶段接近结束时。
Then, as the pulsar nears the end of the stream, a messy disk briefly returns, this time spinning in the opposite direction. And then it, too, disappears as the pulsar exits. In all, the pulsar takes about four days to transit the stream.
然后，当脉冲星接近流的末端时，一个混乱的圆盘会短暂返回，这次以相反的方向旋转。然后它也随着脉冲星的退出而消失。总的来说，脉冲星大约需要四天的时间才能穿过河流。
“The BP Crucis system is an ideal laboratory for studying wind-fed pulsar accretion, and XRISM’s sensitive, high-resolution Resolve spectrometer is an ideal instrument for advancing our understanding of the processes involved,” said Brian Williams, the mission’s project scientist at NASA Goddard.
“BP Crucis 系统是研究风力脉冲星吸积的理想实验室，而 XRISM 灵敏的高分辨率 Resolve 光谱仪是加深我们对所涉及过程的理解的理想仪器，”NASA 戈达德中心该任务的项目科学家布莱恩·威廉姆斯 (Brian Williams) 说。
To learn more about the XRISM mission, visit:
要了解有关 XRISM 使命的更多信息，请访问：